1. Field of the Invention
The present invention relates to a swivel assembly of a vehicle seat, and more particularly to a swivel assembly which is not loosened during swivel thereof due to size errors or the like occured in manufacture and which places an upper plate at a predetermined position reliably.
2. Description of Related Art
Recently, a swivel assembly allowing a front seat to be swiveled to confront a rear seat is adopted in one box cars or the like. Examples of the swivel assembly of a vehicle seat are described below. The one disclosed in Patent Publication Hei8-11600 is described below as a first conventional swivel assembly with reference to FIG. 32. The ring-shaped lower plate 1A L-shaped in section is fixed to a floor side member such as a seat track or the like. The sliding portion 11A inverted U-shaped in section is formed at the top of the vertical wall of the lower plate 1A. The ring-shaped upper plate 2A U-shaped in section is fixed to a seat side member such as a seat cushion frame or the like. The upper plate 2A is bent downward to form the corner 21A at its inner circumferential end. The ball 3A is held between the corner 21A and the inclined surface of the sliding portion 11A to support the upper plate 2A rotatably on the lower plate 1A. The bracket 4A having the slidable portion 41A U-shaped in section is fixed to the upper plate 2A. The slidable portion 41A of the bracket 4A is slidably installed on the sliding portion 11A of the lower plate 1A through the resinous member 5A.
The swivel assembly disclosed in Japanese Patent Publication Hei No. 6-87364 is described below as a second conventional swivel assembly with reference to FIG. 33. The ring-shaped lower plate 1B fixed to a floor side member is bent to form the first corner 13B on the inner circumferential portion 11B bent upward. The upper plate 2B fixed to a seat side member is bent to form the second corner 23B confronting the first corner 13B, and the third corner 24B on the inner and outer sides of the inner circumferential portion 21B bent upward. The ball 3B is held between the first corner 13B and the second corner 23B to support the upper plate 2B rotatably on the lower plate 1B. The ring-shaped set plate 4B is fixed to the inner circumferential portion 11B of the lower plate 1B. The outer circumferential end of the set plate 4B is bent downward to form a fourth corner 44B confronting the third corner 24B. The ball 5B is held between the third corner 24B and the fourth corner 44B.
In the first conventional swivel assembly, the ball 3A is held between the corner 21A and the inclined surface of the sliding portion 11A to place the upper plate 2A in position and prevent the upper plate 2A from being loosened. However, the load of the seat is applied to the ball 3A through the upper plate 2A. Thus, the inclined surface of the sliding portion 11A is worn with the use of the seat. As a result, the upper plate 2A drops and the resin member 5A separates from the inner circumferential surface of the sliding portion 11A and consequently, the upper plate 2A is loosened vertically.
In the second conventional swivel assembly, the ball 3B held between the first corner 13B and the second corner 23B receives the load of the seat through the upper plate 2B, and the upper plate 2B is placed in position and prevented from being loosened vertically by means of the cooperation of the ball 3B, the first corner 13B, and the second corner 23B, and the cooperation of the ball 5B, the third corner 24B, and the fourth corner 44B. However, the vertical walls forming the first through fourth corners 13B, 23B, 24B, and 44B are likely to have errors occured in press molding, thus forming clearances between the ball 3B and the vertical walls of the first and second corners 13B and 23B and between the ball 5B and the vertical walls of the third and fourth corners 24B and 44B, which causes the upper plate 2B to be horizontally loosened. Further, because the load of the seat is received by the ball 3B positioned distant from the load-applied side, the upper plate 2B is liable to be deformed and the swivel assembly has a disadvantage in its strength. In addition, the load-applied side of the upper plate 2B drops with respect to the ball 3B owing to the load of the seat caused by the deformation of the upper plate 2B. Consequently, a clearance is formed vertically between the ball 5B and the third corner 24B as well as the fourth corner 44B, thus causing the upper plate 2B to be loosened vertically.